Optical communication equipment often employs one or more micro-electromechanical systems (MEMS) devices. A typical MEMS device may include an array of micro-machined mirrors, with each mirror being individually movable in response to an electrical signal. Such an array may be employed in an optical cross-connect, in which each mirror in the array receives a different beam of light, for example, from an input optical fiber. The beam is reflected from the mirror and can be redirected to a different location, e.g., a location at which an output optical fiber is located. The particular output fiber that receives the redirected beam may be selected by rotating the mirror. Other optical applications for MEMS devices include wave selective switches, add-drop switches, wavelength attenuators, and wavelength blockers. Non-optical applications are also possible.
One problem with prior art MEMS devices having relatively large mirrors, e.g., between 100 μm and 400 μm in length and between 30 μm and 70 μm in width, is that the height of the gap between the mirror and the corresponding actuating electrode(s) has to be relatively large, i.e., greater 8 μm, to achieve relatively large, e.g., about 10 degree, rotation angles. However, an 8 μm gap height is the best that can be achieved with surface micromachine technology, which is a simple and low cost fabrication technique.
U.S. Pat. No. 6,781,744, which is incorporated by reference as if fully set forth herein, discloses a MEMS device having a movable mirror and a movable actuator plate mechanically that are coupled together such that a relatively small displacement of the plate results in rotation of the mirror by a relatively large angle. In one exemplary arrangement, the mirror and actuator plate are supported on a substrate. The actuator plate moves in response to a voltage difference applied between a) an electrode located on the substrate beneath the plate and b) the plate itself. One or more springs attached to the plate provide a counteracting restoring force when they are stretched from their rest positions by the plate motion. The mirror has a handle portion configured as a lever arm. A spring attached between the actuator plate and the handle portion transfers the motion of the actuator plate to the mirror such that, when the actuator plate moves toward the substrate, the spring pulls the handle portion to move the mirror away from the substrate. Advantageously, relatively large mirror rotation angles may be achieved using the relatively small displacements of the actuator plate that can be achieved using surface micromachine technology.
In another exemplary arrangement disclosed in U.S. Pat. No. 6,781,744, a MEMS device has first and second plates, each supported on, and positioned offset from, a substrate. The second plate is rotatably connected to the substrate. The connection defines a rotation axis and first and second portions of the second plate including its opposite ends with respect to the rotation axis. One end of the first plate is movably connected to the first portion of the second plate, while the other end of the first plate is connected to the substrate.
Disadvantageously, U.S. Pat. No. 6,781,744 only teaches how to achieve rotation by a relatively large angle around a single axis.